Electronic modulator fob constant



R. E. SHELBY Aug. 29, 1939.

ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION Filed Sept. 14, 1936 5 Sheets-Sheet l lNPl/T 1 INPUT 2 N 0M mm Em A ,-F/Rsr ANODE SCREEN GRID 515677305 MTIC DEFLECTING T- l. t 1i u u v TP/ #9 P1 P;

INVENTOR ROBERT E. SHELBY BY 2% 4 Fig 23 ATTORNEY R. E. SHELBY Aug. 29, 1939.

ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION '5 Sheets-Sheet 2 Filed Sept. 14, 1956 INVENTOR ROBERT E. SHELBY ATTORNEY Aug. 29, 1939. R. E. SHELBY ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION,

Filed Sept. 14, 1936 5 Sheets-Sheet :5

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W CARR/ERWAVE P u- 2 A 2 AMPLITUDE I MODULATOR V S/NUSO/DAL VOLTAGE MODULATION SUPER-SONIC FREQUENCY SIGNAL HJHUHWJHUWILM flllMMHHflllll MM INVENTOR ROBERT E. SHELBY ATTORNEY 5 Sheets-Sheet 4 R. E. SHELBY Filed Sept. 14, 1936 llllllllllh Aug. 29, 1939.

ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION rlh- ,;li|||:|||||u|a|u|a R. E. SHELBY 2,173,150

ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION Aug. 29, 1939.

Filed Sept. 14, 1936 5 Sheets-Sheet 5 CATHODF STREAM +3 CATHODE CATHODE STREAM B CATHODE NVENTOR ROBERT E- Patented Aug. 29, 1939,

umrs s'rs ELECTRONIC MODULATOR FOB CONSTANT FREQUENCY VARIABLE DOT TRANSMIS- SION Robert Evart Shelby, Teaneck, 'N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 14, 1936, Serial No. 100,627

12 Claims. (01.179-171) In the past facsimile experimenters have made use of a system of modulation in which the radio frequency carrier is modulated, or keyed, by a fiat-topped supersonic wave of constant amplitude which has complementary, but not necessarily equal, variations in its positive and negative areas that are proportional to the modulation signal. Since the completeperiod of the supersonic wave remains constant while the rectangular dots" or areas, comprising its positive and negative portions, vary in accordance with the modulation, this method has been given the name Constant frequency variable dot, or CFVD, modulation, that is, a wave of constant frequency whose positive and negative alternations vary relatively in length in accordance with modulating signals. More recently this same idea has been applied by Kell to the transmission of sound programs. The chief advantage claimed for the system is that it permits the use of voltage limiters in the receiver and thus gives a higher signal to noise ratio than is obtained when using the usual system of amplitude modulation under the same conditions. No attempt will be made here to discuss the merits of the system. This application is intended only to disclose a novel method of and means for producing CFVD modulation which it is believed has certain advantages over the methods now used.

In describing my invention reference will be made to the attached drawings. In the drawings,

Figures 1 and 1a illustrate one form which the plate or target anode may take and the relation of the same to the other electrodes of an electron discharge gun or cathode ray tube used to produce CFVD modulation in accordance with my invention;

Figure 2 shows schematically the essential elements of my novel circuit for producing and applying potentials to the deflecting plates of an electron gun as illustrated in the prior figures and the mode of connecting the output of the novel circuit to the pairs of deflecting plates in. an electron gun having a novel plate or target anode arranged in accordance with the present invention; I

Figure 2a illustrates a phase shifter used in the circuit of Figure 2;

Figures 3a, 3b, 3c and 4 are curves illustrating the character of the output of an electron gun with an anode as indicated in Figures 1 and 1a when the deflecting plates are excited as indicated in Figure 2;

Figure 5 shows schematically the essential elements of a complete CFVD modulator arranged in accordance with my invention;

Figure 6 shows a modified anode structure; while Figure ,7 is a curve representing the output of a system when the anode is as shown in Figure 6;

Figures 8, 9, and 10 illustrate modified forms of final or target anodes.

In my United States application #72916 filed April 6, 1936, entitled Electronic modulator and method of modulation, a novel circuit and novel electron discharge device for producing phase and amplitude modulation is described. In the present application and in the aforesaid application I use a novel electron gun or tube having a special target anode for converting amplitude modulated wave energy applied to pairs of defleeting plates into energy of the desired character for signalling purposes.

The term electron gun here as in the prior application, has the meaning given to it by I. G. Maloff and D. W.-Epstein in their paper entitled Theory of electron gun appearing in the Proceedings of the IRE, December 1934, page 1386. The circuit and device to be described here is in many respects similar in arrangement and operation to that disclosed in the said application. Here, however, the configuration of the final anode in the electron discharge device is different than that of the aforesaid application in order that CFVD output may be obtained in place of phase or amplitude modulation. Here, as in the said application, the tube illustrated diagrammatically in Figures 1 and 1a consists essentially of an electron gun 4, two setsof electrostatic deflecting plates 6 and}, and a final anode it]. The target anode II] is of special design. Figure 1a shows one form which the final anode l0 may have for production of CFVD modulation. The final anode or target Ill consists of two curved plates It and it, having the complementary boundaries indicated by Figure 1, upon which the electrons from the electron gun impinge. The electrodes It and It may consist of metallic plates or meshes or metallic deposits on the tube envelope or a surface supported in said tube. Where the electrodes i6 and 16 are of mesh 9. collecting electrode, not shown, may be located back of the targets and .properly charged relative to the other electrodes.

In order to obtain a CFVD signal the plates is and I6 are caused to have the shape or form shown wherein the outer periphery of one side of IS follows a curve defined by r==-a0--6 while the adjacent inner periphery of ll follows a curve defined by r==a0+5. The other outer periphery of Hi may be defined by r=--a0-6 while the periphery or edge of i4 adjacent said last boundary is defined by r=aa+6. In these equations r is the radial distance from the origin 0 to any point on the edge of the plate. 0 is the angular displacement of the same point from a selected datum line which is the same for each curve; while a and a are design constants, the latter depending on the spacing of the anode sections. In the modification illustrated the datum line for the curves of the equations is shown by the broken line X. The equations given for the anode contours were departed from sufllciently near the origins to prevent the anode sections from becoming short-circuited.

In operation, the electron gun is controlled and focussed by adjusting the direct current potentials applied to the cathode, and to the control grid by 20, and to the screen grid and first anode, by 22, just as in the case of oscillograph tubes and kinescopes. The electron stream is sharply focussed on the final anode l0 and when there is no voltage applied to the electrostatic deflecting plates 6 and 8 it strikes the exact geometrical center of the final anode In. The deflecting voltages, the nature of which and the manner of production of which will be described more in detail hereinafter, are such that they cause the electron stream to trace out a circle on the flnal anode lo, the diameter of the circle being a variable which is directly proportional to the instantaneous value of the modulation signal on the wave energy applied to the deflecting plates. When the plates 6 and 8 are excited by proper voltages there will appear in Za a CFVD voltage characteristic of the modulating potentials used in producing the deflecting voltages. The deflecting voltages are preferably sinusoidal and of the supersonic frequency selected for the CFVD transmission. The deflecting voltages are obtained by phase displacing two portions of amplitude-modulated wave energy. The manner in which the deflecting voltages are produced and applied to the plates 6 and 8 is shown in Figures 1 and 2 and will now be described.

In Figure 2 voltages of substantially constant frequency and of sinusoidal form are supplied from any source to a modulator 2| of any known type. The oscillations may be produced by an oscillator of the crystal or line controlled type or of any other type, the only requirement being that they be of substantially constant frequency and constant alternating current amplitude. The modulator 2| may be of any type having the desired characteristics. The wave of sinusoidal form supplied to 2| is modulated in amplitude in accordance with the desired modulation signal impressed from any source on 2|. The output of the modulator 2| is connected to an amplitude regulating potentiometer P1 which is connected by a movable point to a phase shifting network 23. -This network may take any suitable form, the essential feature being that the output thereof supplies two portions of the amplitude modulated wave in phase displaced relation. The amplitudes of the portions are substantially equal. Where the plates 6 and 8 are at right angles with respect to each other the phase displacement of the deflecting voltages should be substantially Other angular relations between the deflecting plates requires other phase relations between the deflecting voltages. One

output from 23 goes directly to one set of defleeting plates. The other output from 23 goes to a potentiometer P2 connected to the other set of deflecting plates. A preferred form of phase shifter is shown in Figure 2a. In this phase shifting circuit the amplitude modulated radio frequency or carrier frequency waves are applied toinput terminals and from said input terminals to a resistance 30 in series with condenser 32. By adjusting the condenser 32 and selecting the value of 30 the desired phase relation between er and e: can be produced. The oscillations in 2| may be modulated in amplitude by facsimile signals, by keyed impulses, by voice frequencies, television or any other type of signals to produce constant frequency variable dot characters.

For a more detailed explanation of how the system works refer now to Figures 1, 1a, 2, 2a, 3a, 3b and 30. First with no modulation input to 2| the phase shifting network in 23 and potentiometer P2 of Figure 2 are adjusted so that the electron beam of the gun 4 describes a circle on the target or final anode It. If the potentiometer P1 is adjusted so that this circle is of the size designated by c1 in Figure 1a then the voltage appearing across ZA, 1. e., the output voltage will be as shown in Figure 3a. It will be noted that the electron stream passes from one segment, say ll, of the target anode to the other, say segment l8, and from the latter to the former at points 111 and 111', which are 180 apart. This means that the positive and negative portions of each cycle of the flat-topped supersonic output voltage wave are equal, and this adjustment therefore corresponds to zero modulation. If now the two deflecting voltages from 23 are decreased in amplitude to almost zero by changing potentiometer P1, all other controls being left the same, the locus of the end-point of the electronstream will be c: of Figure 1a, and the voltage across ZA will be as shown in Figure 3b. The electron stream 'now passes from one segment, say H, of the anode to the other, say segment l6, and from the latter to the former at points p: and p2. Likewise if the potentiometer P1 is adjusted to give voltages almost double those which produced the locus 01 then 03 will be the new locus, the electron stream will pass from one anode segment to the other at points pa and pa and the voltage appearing across ZA will be as shown in Figure 30. Now if P1 is reset so that the electron circle falls on 01 and amplitude modulation of almost percent is then applied to the deflecting voltages in the manner indicated by Figures 1 and 2 the locus of the end-point of the electron stream will expand and contact between the limits 0: and O3 and the output wave will change its delineation, in accordance with the modulation signal between the two extremes shown in Figures 3b and 3c, the delineation of Figure 3a corresponding to zero modulation voltage. In this system adjustment of circuit constants and monitoring of the system is facilitated by coating the target anodes or plates with willemite or other substance which fluoresces under the bombardment of the electron stream.

This device may be used to convert potentials of any frequency of sine wave form into voltages of flat topped wave form of equal frequency the duration of the dots of which can be adjusted through a wide range. This is accomplished by applying an unmodulated wave of sine wave form to P1 and adjusting the same to make e1 and 62 or the desired value. The flat topped wave so produced is of wide application in the radio and allied arts and is of particular value for television pictures and synchronization.

Figure 4 shows what a CFVD modulated fiat topped supersonic wave looks like. In this example the modulation is a sine wave the frequency of which is & that of the supersonic wave, and the percent of CFVD modulation is 75. For radio transmission this CFVD modulated voltage wave may be used to amplitude modulate or key a radio frequency carrier wave which may be used for signalling in any known system. A complete modulating system arranged in accordance with my invention has been shown in Figure 5 and will now be described.

Referring more in particular to Figure 5, 60 is an oscillation generator of carrier wave frequency of any type which produces oscillations substantially constant in frequency and amplitude. The oscillatory energy from 50 is impressed by way of a coupling condenser 62 on the control grid of an electron discharge device M. The electron discharge device 65, which may be of any type and is for purposes of illustration shown as being of the pentode type, is supplied with control grid potentials from a source 5! by way of a resistance 83. The anode electrode of tube id is connected with a parallel tuned circuit 56.

The circuit 46 may be tuned to the frequency of the oscillations from $0 or to a harmonic thereof. The screening electrode of tube at is supplied with operating potentials by way of a resistance 55, the terminals of which are connected to ground as shown by radio frequency icy-passing condensers BP. The pentode 54 may be replaced by any other tube having appropriate characteristics, for example, a triode may be utilized here, in which case the circuits may include neutralizing means. In the present case neutralization is unnecessary because the screening electrode shields the output circuit 56 from the input circuit and the source so. The tube 44 which also serves as a modulator, may multiply the frequency of the oscillations from lii in which case 56 is tuned to a multiple frequency.

The inductance of 66 forms the primary winding of a transformer, the secondary winding of which is connected in parallel with a tuning condenser to provide a tuned circuit 55. One terminal of the tuned circuit 55 is connected to ground by way of a resistance 53 and is also connected directly to one plate of one of the sets of deflecting plates 5 and 8, say of plates 6. The other terminals of the tuned circuit 55 is connected with a phase shifting circuit 58 comprising inductance 5i shunted by a variable condenser 59 and a variable resistance 66. One end of the phase shifting circuit 58 and the said other terminal of 55 is connected as shown to ground by way of a resistance 5! and also con nected directly to one of the plates of the other set of deflecting plates, say plates 8. maining terminal of the phase shifting circuit 58 is connected. to the remaining deflecting plates of each of the pairs of plates 6 and 8. These remaining deflecting plates are also connected to ground by way of resistances 6| and 62. This last terminal of the tuned circuit 58 is also connected to one terminal of 55 by a variable con denser 5?. Thus, we have a series circuit including the capacity between the plates 6, the tuncomparison to the impedances of 58 and 81. The

The re-' capacity between the plates 6 is supplemented by the capacity of the condenser M. This phase displacing circuit may be made the equivalent of a pure resistance in series with a capacity bridged across the driver circuit 55 since the circuit 58 and the capacity of the other set of deflecting plates 8 may be tuned to resonance at the frequency of the oscillations applied to 55 and thereby made to represent a pure resistance at this frequency.

The variable resistance 60 is used to control the amplitude of the potentials applied to the deflecting plates 8. When adjusted in such a manner this phase shifting circuit is equivalent to the circuit shown in Figure 2a. Any other appropriate phase shifting means may be used.

Up to, this point I have described means for applying high frequency or carrier frequency oscillations in phase displaced relation between the plates 8 and 6 of the electron discharge gun of the present invention. I will now describe the means for amplitude modulating the oscillations applied to said plates to thereby control the electron stream in its radial path of rotation on the target anode.

Modulating potentials may be supplied from any source to the primary winding of the audio frequency transformer AF]? the secondary winding of which is coupled as shown to potentiometer resistance PR. A point on the potentiometer resistance PR is connected as shown to the control grid of a modulation frequency amplifier 6B. The output of the modulation potential amplifier 68 is connected as shown to a direct current source by way of an audio frequency reactor 69. The anode of 88 is also coupled by way of a blocking condenser 10 to the tuned circuit 46 connected to the anode of the tube 44.

anode of M to thereby accomplish amplitudemodulation of the oscillations from 40 to 54. These amplitude modulated potentials are displaced in phase in 55, 58, etc., as described above and applied to the pairs of plates 6 and 8 as described heretofore, to produce CFVD potentials in Za connected with the anode ll) of tube i.

The CFVD potentials in Za or in one portion thereof may be utilized in any manner. For example, they may be used for modulation purposes in which case they may be impressed on a modulation frequency amplifier 16 to modulate in 18 high frequency oscillations of constant frequency from 80. The modulated high frequency oscillations in 78 may also be amplified therein and impressed on a radiating system 80 or a transmission line 8|.

The power output of the electron tube or gun 4 of Figure 5 and of the preceding figures may be increased by providing a second anode 90, located adjacent the target anodes in. In practice may be a conducting arrangement located in the tube or may consist of a deposit or coating on the tube envelope. The electrode 90 is maintained at a potential more positive than that applied to electrode Ill by source 9|. The source 9| and the source connected with the electrode to may be of any type and may in practice be a single source. The anode or collecting or return electrode 90, collects the electrons emitted from the target anode ID by the phenomena of secondary emission occurring when the primary cult Za and since the secondary emission may be madev greater than the primary emission; the current 'output may obviously be increased. When this is accomplished to the desired extent, the number of stages between the circuit Za and the modulator 18 may be materially reduced. The manner in which this phenomenon isvused to enhance the power output, has been disclosed more in detail in Hendrick United States application #673,5'70 filed May 30, 1933.

In a modified form of CFVD system transmission instead of transmitting the complete full length dots, very 'much shorter, sharp impulses are transmitted at the beginning and end of each dot. The operation of this modified CFVD system (sometimes referred to as timed impulse transmission) will be obvious from the foregoing description of my preferred modification as will its merits. Such a system requires a much wider radio frequency channel than the ordinary CFVD signalling system described above, which itself requires a hand many times as wide as ordinary amplitude modulation for the same audio frequency response, and requires a special receiver, whereas theordinary CFVD signal may be received with the usual amplitude modulation receiver although there is no appreciable gain in signal to noise ratio unless limiters are used in the receiver. However, when the short sharp impulses are used rather than the usual CFVD for a given average power input to the transmitter the signal to noise ratio at the receiver is much higher than for the ordinary CFVD method of transmission.

Figure 6 illustrates one form of fin'al or target anode for the electronic modulator or electron gun modulator which will give the modified CFVD modulation outlined above. It is practically the same as the one shown in Figures 1 and 1a except that at third target anode segment 5 has been added between the segments l4 and Hi. The electrode H5 is electrically independent of the other two segments and is connected to the high voltage direct current supply source through an additional coupling impedance Zn, across which the output appears comprising short sharp impulses.

Thus, as the electron stream passes from ll, say to It, it first impinges on 5 and produces in Zn a short sharp impulse of constant duration for all radial positions of the stream. Likewise, when the stream passes from l6 to It a short sharp impulse is produced so that each of the usual CFVD impulses is preceded and succeeded by the short impulses of equal duration. The form of the wave is shown in Figure 7.

It is noted in passing that the voltage appearing across Zn in Figure 6 is similar to that produced across ZA of Figure 1 being modified only by the action of I I5 and Zn as described above, and it is thus apparent that this one form of anode might be utilized for either type of CFVD modulation. The step by step analysis of the principle of operation will be omitted since it is so similar to the one given above for the anode of Figure 1. 04 is the zero modulation circle and c5 and Co are the limits between which the electron circle moves when the modulation is 75 per cent. Figure 7 is an example of 75 percent modulation by the modified CFVD method. The modulating signal in this case is a sine wave. ,5 the frequency of the dot wave. For radio transmission the wave of Figure '7 is used to amplitude modulate or, optionally, to key the radio frequency carrier. For example, the modulated wave in Figure '7 may be applied to the grid electrode of a radio frequency amplifier to control its bias and key the tube.

Obviously, many variations are possible in the construction and utilization of this electronic modulator. To mention but two electromagnetic instead of electrostatic deflection of the electron beam may be used, and the size of the electron circle may be varied by introducing the modulation signal into the, anode supply circuits instead of modulating the deflecting voltages with it.

While I have shown the plate 16 of Figure 1a and plates l6 and 5 of Figure 6 as being located within plate I 4, I contemplate the use of target anodes wherein I4 is a complete circle plate, while it is disposed in front of H as shown in Figure 8. This structure simplifies production because only one plate, i. e., l6, needs to be formed in accordance with my equation which may then be modified is shown in Figure 8. With this form of final target the wave form is improved because the electron stream falls substantially directly on I4 when it leaves I6 and vice versa. In other words, the constant 6 is removed from the equa-v tion. The target of Figure 9 is particularly adapted to production of CFVD as is the anode or target electrode of Figure 1a. In this arrangement electrode ll may also be utilized as the collecting electrode to supplement or replace the action of electrode of Figure 5.

The same advantages of production can be obtained by using a target anode as illustrated in Figure 9 wherein the electrode i6 has a heartshaped opening therein and the electrode l4 may have any peripherical contour so long as it completely covers said heart-shaped opening in It. This target arrangement is also particularly adapted to the production of CFVD.

It will be noted that in Figures 8 and 9 the electrode formed in accordance with my equation can follow the latter exactly from 1:0 out since there is no radial spacing necessary between the edges of the plates to prevent short circuiting as in Figures 1a and 6.

For the production of modified CFVD or tuned impulse the target I I5 may be placed in front of a plate M as shown in Figure 10.

In each modification the electrodes l4 and I6 and I4 and I6 and I I5 may be coatings or deposits on the tube envelope properly separated by insulating material or supported thereby.

I claim:

1. In signalling apparatus comprising a cathode ray tube having an emission element, pairs of deflecting plates, and a target anode comprising at least two conductively separated conducting elements or surfaces one of which is heart-shaped and located wholly within the area of the other, the method of producing constant frequency variable dot wave energy, the duration of the dots of which are characteristic of signalof deflecting plates, a target anode comprising two conducting elements or suriaces located around the focal point of said stream, a portion of the boimdary of one of which conducting ele- .ments or plates is defined by r=:a9+6, a portion-of the boundary of the other of which plates -from the electron stream focal point; a and 6 are constants, and 0 is the angular deviation from a straight line through the focal point where r is substantially zero; the method of signalling which includes the steps of producing wave energy modulated in accordance with signal voltages separating said modulated wave energy into two phase displaced portions, impressing said phase displaced portions on said deflecting plates to control 'the path of said stream in accordance therewith, and producing alternating currents the positive and negative portions of which are of a time duration equal to the time during which said stream falls on the elements or plates.

3. The method of producing constant frequency variable dot energy, the duration of the dots of which are characteristic of signal voltages which includes the steps of producing an electron stream of constant intensity, rotating the path of said stream in accordance with phase displaced modulated carrier potentials, and producing currents characteristic of the deflection of said rotated stream.

4. The method of producing high frequency oscillations modulated in accordance with constant frequency variable dot signals which includes the steps of producing an electron stream of constant intensity, producing phase displaced amplitude modulated oscillatory energies, deflecting the path of said stream in accordance with said phase displaced modulated oscillatory energies, producing currents characteristic of the deflection path of said stream and modulating the high frequency oscillations in accordance with said currents.

5. In a constant frequency variable dot modulation system, a discharge device having an electron stream emitting system, a target anode including conductively separated plate elements, means for modulating carrier wave oscillations in accordance with signalling potentials, means for phase displacing said modulated carrier wave oscillations, means for deflecting said stream relative to its normal path in accordanc with said phase displaced modulated carrier wave oscillations, an output circuit connected with said target elements, a high-frequency oscillator and means coupling said output circuit to said high frequency oscillator.

6. In a constant frequency variable dot modulation system, a discharge device having an electron emitting electrode, a target electrode comprising two conductively separated elements and a plurality of pairs of deflecting electrodes adjacent the path between said emitting electrode and said target electrode, means for producing phase displacedamplitude modulated wave energy and impressing the same on to different pairs of deflecting electrodes, an output circuit coupled with saidtarget elements, a high frequency oscillator and means for coupling said output circuit to said high frequency oscillator.

7. In a constant frequency variable dot modulation system, a discharge device having an electron emitting electrode, a target electrode comprising two unlike conducting elements conductively separated each from the other, an output circuit connected between said elements and connected to said emission element, pairs of deflecting plates adjacent the path of emission of said stream, a source of modulating potentials a source of oscillations of carrier wave frequency, means for modulating said oscillations in accordance with said modulating potentials, and means for deriving phase displaced modulated energies from said modulating means and impressing the same on difierent pairs of deflecting plates.

8. In a modulation system, a discharge device having an electron emitting electrode, a target electrode comprising two plates, a portion of the boundaries of one of which plates is defined by 1=a0+6 and another portion of the boundaries of said one of said plates being defined by r=a0+6 where r is the radius from the electron stream focal point, a. and a are constants, and 0 is the angular deviation from a straight datum line to said focal point along which r= substantially zero, pairs 01' deflecting electrodes adjacent the path between said emitting electrode and said target electrode, a source of modulating potentials, a source of oscillations, means for modulating said oscillations in accordance with said modulating potentials, and phase displacing circuits coupling said last named means to said deflecting plates and an output circuit coupled with said target electrodes.

9. In a modulation system, a discharge device having an electron emitting electrode, a target electrode comprising two plates a portion of the boundaries of one of which, is defined by T=id0-6 and a portion of the boundaries of the other of which 'r=;*:a0+a where r is the radius from the electron stream focal point, a and 6 are constants and 0 is the angular deviation from a straight datum line to said focal point along which substantially zero, pairs of deflecting electrodes adjacent the path between said emitting electrode and said plates, a source of modulating potentials, a source of oscillations, means for modulating said oscillations in accordance with said modulating potentials, and phase displacing circuits coupling said last named means to said deflecting plates and an output circuit coupled with said target electrodes.

10. In signalling apparatus comprising a cathode ray gun having an electron emitting element, pairs of deflecting plates in the path of emission from said element and a target anode comprising two collecting elements one of which is heartshaped and located wholly within the area of the other and an output circuit connected between said elements and said emission electrode, the method of converting wave energy of symmetrical form into a flat topped wave energy which includes the steps of producing an electron stream of constant intensity, producing phase displaced voltages characteristic of said energy of symmetrical form and deflecting the path of said stream in accordance with the strength of said voltages and producing currents characteristic of the time which said stream falls on the plates of said target anode.

11. In signalling apparatus comprising a cathode ray gun having an electron emitting element, pairs of deflecting plates in the path of emission from said element and a target anode comprising two collecting elements one of which is heartshaped and located wholly within the area of the other and an output circuit connected between said elements and said emission electrode, the method of converting wave energy of symmetrical form into a flat topped alternating current wave the duration of the positive and negative portions of which may be varied, which includes the steps of producing an electron stream of constant intensity, producing phase displaced voltages of ad- 'Justable amplitude and characteristic of said energy of symmetrical form and deflecting the path of said stream in accordance with the strength of said voltages and producing currents characteristic of the time which said stream falls on the respective plates of said target anode.

' 12. In a constant frequency variable dot modulation system, a discharge device having an electron emitting electrode, a target electrode comprising two plates, one of which is disposed between the other plate and the emission element 15 and has an opening therein the boundaries 01' electrode and said plates, a source of modulating potentials, a source of oscillations, means for modulating said oscillations in accordance with said modulating potentials, and phase displacing circuits coupling said last named means to. said deflecting plates and an output circuit coupled with said target electrodes.

ROBERT EVABT SHELBY. 4 ll 

